Connecting Two Worlds: BSBO in Costa Rica

Male Wilson's Warbler

For five weeks during January and February, 2016, BSBO's Julie Shieldcastle worked with Costa Rica Bird Observatories banding neotropical migrants at two banding sites. Here is Julie's summary of the experience.

We have a tendency to think of the birds that pass through NW Ohio in the spring and fall as "our birds." Of course, some of them will stay in Ohio to breed, but the majority spend most of their time elsewhere, either breeding, during migration, or wintering in some habitat south of the U.S. border.

While in Costa Rica, I had the opportunity to observe and/or capture with mist nets some of “our birds.”  My goal was to observe some of the molt strategies of these neotropical migrants during the alternate molt period we only get a small glimpse of. Just as not all of our birds breed in the same habitats up north, birds utilize a variety of wintering habitats down south. In five weeks of field work, I couldn't even consider relating to you where all species reside in winter. It was a small window of time and limited captures of migrants to make much sense of these intricate processes, but a valuable experience just the same. And it was educational to visit two distinctive habitats: the warm and humid Caribbean, and the cooler, damper cloud forest in the mountains of Cerra de Muerte.
  

Chestnut-sided Warbler still in basic plumage

Chestnut-sided Warblers (CSWA), from my brief experience, hang out along the Caribbean Coast in mid-January. There were quite a few of them observed foraging in the trees in the fragmented forest areas of Tortuguero. (It was interesting to find no evidence that the winter molt had even begun - which fits with this species' strategy of molting while in migration.) 

Summer Tanager male molting into Alternate Plumage

Summer Tanagers were found in both sites I visited. From the literature, males and females of migrant species often winter in different locations, and different habitats, just as they do on the breeding grounds. Their behavior is just as complex here on the wintering grounds as it is on the breeding grounds and possibly their migratory stopover locations, making it difficult to develop sound conservation strategies.

One discovery that still stands out for me was when we weighed Chestnut-sided Warbler at the Tortuguero site. It had no fat and weighed 6.8 grams. This was a bit of a shock to me, since when we capture them here in Ohio during migration, they do have some amount of fat reserves and usually weigh around 8-9 grams. I was concerned the scale to weigh the birds was not working correctly, but it was checked and was calibrated properly. So, was the CSWA at a normal weight for the wintering area? What happens when it is time to migrate? Is the habitat good enough to build fat reserves for migration? Is there a critical level of volume or quality of habitats to provide enough food resources for them to make a long distance migration? 

Tennessee Warbler in the cloud forest mountains of CR

The map of the Tennessee Warbler in the Costa Rica bird field guide shows them found throughout all of the country. Of the two places I was stationed, I only observed them in the mountains. Could this represent a habitat shift, or are different habitats needed at different times during the winter and staging periods? Also found in the cloud forest and associated cow pastures were Black-and-white Warblers (alternate molt completed already), Golden-winged Warblers (GWWA), Wilson's Warblers, and a Louisiana Waterthrush.

Black-and-white Warbler Male

Louisiana Waterthrush captured in the fragmented areas of the cloud forest 

We captured a female Golden-winged which surprised the GWWA project leader. They thought only males wintered in the mountainous area we were in. Another reminder of the fact that new information is gathered all the time, and that as habitats and bird populations change, more research is required to keep us informed on the needs of birds.

Female Golden-winged Warbler

I had many adventures and some very eye-opening experiences, but one overlying theme throughout my travels was that we all live on this planet together. While we do have a long way to go in protecting habitat right here in our own country, our birds are spending a large part of their lives in other countries. We should never lose sight of the fact that if we are going to protect birds, we've got to protect and conserve habitat for birds throughout their life-cycle. 

In our promotion of birds at BSBO, we are fond of declaring that "BIRDS RULE." This thought took on a new meaning during my trip. Maybe, just maybe, if birds really did rule, this planet would be a little bit better for it.